The present inventin relates to a method and an apparatus for automatic cooking in a microwave oven which is capable of executing automatic cooking in an optimal state by detecting an inflow air temperature, an outflow air temperature, and a weight of food to be cooked and calculating a cooking time using the detected signals relating to the inflow and outflow air temperatures and the weight of food in a fuzzy control even in the case of a continuously using the microwave oven.
Various types of cooking methods and apparatuses for use in a microwave oven are well known in the art. One conventional microwave oven is illustrated in FIG. 1. As shown in FIG. 1, the conventional microwave oven comprises a microcomputer 1 for controlling the operation of the whole system, a magnetron driving section 2 for supplying a magnetron driving power upon the control of the microcomputer 1, a magnetron 3 for generating a microwave by being driven by the magnetron driving power of the magnetron driving section 2, a heating chamber 11 for heating the food positioned on a glass tray with the microwave generated at the magnetron 3, a cooling fan motor 4 which is actuated upon the control of the microcomputer 1, a cooling fan 5 for blowing air in the heating chamber 11 by being actuated by the cooling fan motor 4, an outflow air temperature sensor 6, mounted on an outlet 12 of the heating chamber 11, for detecting the temperature of the air which is discharged through the outlet 12, an analog/digital coverter 7 for converting the air temperature signal detected at the outflow air temperature sensor 6 into a digital signal and applying the converted digital signal to the microcomputer 1, a turntable motor 9, mounted below the heating chamber 11, for rotating the glass tray 10 upon the control of the microcomputer 1, and a weight sensing section 8, disposed below the heating chamber 11, for detecting the weight of food and applying the detected weight signal to the microcomputer 1.
With reference to FIGS. 2 and 3, the operation of the conventional microwave oven is described hereinbelow.
Upon pressing a button for automatic cooking in a state that the food to be cooked is positioned on the glass tray 10 within the heating chamber 11, the microcomputer 1 executes a first stage heating operation for a predetermined time(t), as shown in FIGS. 2 and 3, and actuates the cooking fan 5 to blow air into the heating chamber 11 so that the air temperature of the heating chamber 11 can be made uniform. After a predetermined time T1 has elapsed, the microcomputer 1 carries out a temperature, increment setting operation. That is, the current temperature T1 of the air discharged through the outlet 12 of the heating chamber 11 is detected by the outflow air temperature sensor 6 and converted into a digital signal at the analog/digital converter 7. The digital signal of the current temperature t1 is applied to the microcomputer 1 so that the microcomputer 1 can calculate the temperature increment therefrom. When the temperature increment is set, the magnetron 3 is continuously actuated by the magnetron actuating section 2. As time passes, the food positioned on the glass tray 10 within the heating chamber 11 is heated by the microwave and thus the temperature of the air discharged through the outlet 12 becomes high. The temperature of the discharged air is detected at the outflow air temperature sensor 6 and converted into a digital signal by the analog/digital converter 7 and then applied to the microcomputer 1. Accordingly, the microcomputer 1 executes a first stage heating operation until the temperature increment T2-T1 of the outflow air rises to the temperature increment .DELTA.T which has already been established.
In this state, when the temperature increment of the outflow air, i.e., the temperature increment T2-T1 obtained by subtracting the initial temperature T1 from the current temperature T2, arrives the preestablished temperature increment .DELTA.T, the microcomputer 1 finishes the first stage heating operation and calculates a second stage additional heating time t3 to execute a second stage heating operation. That is, the second stage heating time t3 is calculated by multiplying a predetermined value .alpha., which is established in accordance with the type of food, by the first stage heating time t2, and the magnetron 3 is continuously actuated for the second stage heating time t3 to heat the food. When the second stage heating time t3 is complete, the microcomputer 1 stops the operation of the magnetron 3 and the cooling fan 5, thereby completing the cooking.
However, in such an automatic cooking method for use in the conventional microwave oven, there has been a disadvantage in that it is impossible to correctly execute an automatic cooking operation since the temperature increment .DELTA.T becomes dull more than that in case of cooking the previous food when another food is cooked immediately after the previous food has been cooked. That is, when the cooking operation is finished in a state that the outflow air temperature, detected at the outflow air temperature sensor 6, is raised to a predetermined temperature T3, as shown in FIG. 3B, after cooking one type of food, the outflow air temperature T drops down gradually. At this moment, when starting the cooking operation again at the temperature range T4-T8 which is higher than the initial temperature T1, the temperature increment rate becomes low, as shown in FIG. 2C, so that the first stage heating time and the second stage heating time are set too long. Accordingly, the next food to be cooked in the consecutive cooking operation may be excessively heated so that an automatic cooking operation can not correctly be executed. As a result, a non-operation period for about 10 to 30 minutes is required before executing automatic cooking again.